Welcome to

"Our bookcase"


The website of the Dutch author duo Bert Holtes & Wop Sietsma. The digital place for all information about the trilogy BACK-UP.

A thriller series that is not only exciting, but also full of intrigue, action, mystery and shocking revelations, and has already been read in more than 100 countries worldwide.

In Dutch, in German and even in English!

And to get to know our story, the first two volumes are free to read and to give away as e-books.

We invite you to discover this unique trilogy and enjoy an unforgettable reading experience.

Enjoy reading!